22mm pipes instead of 15mm?

[paul.freeland]

Hi,
I have a question regarding my aging potterton combi boiler. All the pipework in my house is 15mm. So on the boiler I have 15mm flow and return pipes, 15mm gas, 15mm dhw and 15mm rising mains water.
The boiler is upstairs in my 2 bed semi.

I need to replace the boiler fairly soon. Which pipes will need replacing, how far back will they need changing, and how much disruption will this cause?

Thanks

Paul

 

[kevplumb]

flow and return should be 22
depending on the length and the gas rate of the new boiler
the gas may need replacing as well

 

[paul.freeland]

Oh dear, thanks for your reply.

How far will the 22mm flow and return pipes need to go? All around the house or just to the nearest rad?

Paul

 

[kevplumb]

if the system is working ok first rad

 

[croydoncorgi]

Hang on....
If whatever new boiler has a minimum flow rate in CH mode, pipe sizing at least up to a bypass possibility may need to be bigger to allow enough flow.

Anyway, if you have 15mm literally everywhere, I suggest you should consider getting separate 22 mm flow and return runs to the upstairs and downstairs. The issue is not only how to avoid killing the boiler. You also need to think about the rate you can deliver heat to the rads.

When the 'standard' boiler setting was hot, hot, hot (eg 80 degrees), this second issue was not so critical. Nowadays, with condensing boilers demanding lower operating temperatures, it is much more important.

If both pipes AND rads are undersized, result will be VERY long warm-up times in individual (or maybe all) rooms.

Doing the calculations is only arithmetic and a PC computer program. Why not download a free Heat Loss program and do the numbers yourself. Then you'll know the actual requirement BEFORE you start spending money.

 

[paul.freeland]

where do I download one of these calculators?

Can I not just find a boiler which will cope with my existing system without too much upheaval? The current potterton lynx does very well at heating the house... It's just unreliable and on it's last legs.

I'm worried that any plumber who comes in to fix the plumbing is going to take me for a ride.

 

[croydoncorgi]

try http://www.quinn-radiators.co.uk/downloads_heatloss.php.

It's 'as-is' software but works adequately, IMHO. Once you've got the numbers for each rad in each room, then you'll need to do a manual calc to work out the pipesizes based on boiler operating temp and sensible figurtes for litres per minute in each pipe. I forgot to mention that if you 'overpump' a system with small pipes to get enough heat around it, it will also be noisy (lots of hissing and whooshing noises in the pipes).